Transistors such as metal oxide semiconductor field effect transistors (MOSFETs) or simply field effect transistors (FETs) or MOS transistors are the core building blocks of the vast majority of semiconductor integrated circuits (ICs). A FET includes source and drain regions between which a current can flow through a channel under the influence of a bias applied to a gate electrode that overlies the channel. Some semiconductor ICs, such as high performance microprocessors, can include millions of FETs. For such ICs, decreasing transistor size and thus increasing transistor density has traditionally been a high priority in the semiconductor manufacturing industry. Transistor performance, however, must be maintained even as the transistor size decreases.
A FINFET is a type of transistor that lends itself to the dual goals of reducing transistor size while maintaining transistor performance. The FINFET is a three dimensional transistor formed in a thin fin that extends upwardly from a semiconductor substrate. Transistor performance, often measured by its transconductance, is proportional to the width of the transistor channel. In a FINFET, the transistor channel is formed at least along the vertical sidewalls of the fin, so a wide channel, and hence high performance, can be achieved without substantially increasing the area of the substrate surface required by the transistor. Additionally, the threshold voltage of a FINFET, which is basically the minimum gate voltage necessary to turn the transistor “ON,” is also a function of the width of the transistor channel and therefore, is determined at least in part by the dimensions of the fin (e.g. height of the fin's vertical sidewalls).
Design and performance requirements vary for a variety of different IC applications. It would be desirable for some of these applications to have the flexibility to form semiconductor ICs having FINFET type transistors with multiple threshold voltages and varying transistor performance. Unfortunately, current methods for fabricating semiconductor ICs with FINFET type transistors often do not lend themselves towards forming dimensionally different fins.
Accordingly, it is desirable to provide methods for forming semiconductor devices that include FINFET type transistors with dimensionally different fins to provide multiple threshold voltages and/or varying transistor performance. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.